1. Field of the Invention
The present invention relates to a management system for collectively controlling various information in a lithographic process employing plural exposure apparatus, and also to the control of exposure apparatus and correction of various information.
2. Related Background Art
The manufacturing process of semiconductor devices or liquid crystal display devices generally contains so-called lithographic process. Such lithographic process is generally an optical process, which starts from coating of a semiconductor wafer or a glass plate with a photosensitive material (photoresist) with a thickness of about 1 .mu.m, and ends with exposure of said photoresist layer to a mask pattern and development of said photoresist layer.
In the device producing sites, a step of coating the substrate with photoresist and a step of developing the substrate after exposure are mostly conducted in an apparatus called coater-developer, and an exposure apparatus is used for transferring a mask pattern onto the substrate coated with photoresist, with precise alignment and with a predetermined resolving power.
In mass production lines for devices, the coater-developer and the exposure apparatus are integrated as an in-line structure. The operator is therefore only required to set a cassette, containing plural unprocessed substrates, into the coater-developer, and all the subsequent steps are conducted automatically.
Also in such production lines, plural exposure apparatus (and coater-developers) are used in parallel manner, in order to improve the efficiency of mass production. In such configuration, in order to improve the working rate of each exposure apparatus, the plural exposure apparatus in a line are collectively controlled by a host computer which overrides the computers in said exposure apparatus.
FIG. 1 is a block diagram schematically showing an example of conventional collective control, wherein blocks EXP1, EXP2, . . . , EXPn indicate exposure apparatus, and blocks CD1, CD2, . . . , CDn indicates coater-developers. Each exposure apparatus EXPn is provided therein with a controlling computer CMP.multidot.En, while each coater-developer CDn is provided with a controlling computer CMP.multidot.Cn. Also each exposure apparatus EXPn is provided with a reticle library RLn containing predetermined plural reticles (masks), and a necessary reticle is automatically loaded according to the instruction by the computer CMP.multidot.En. The coater-developers CDn are equipped with libraries WCL1, WCL2, . . . , WCLn each containing predetermined lots of wafers (usually 25 wafers in a lot) in the units of cassette. In fully automated production lines, however, an automatic transportation robot loads the wafer cassette in automatic manner to a coater-developer which becomes available earliest in time, so that said wafer
cassette library WCLn need not necessarily be integrated as an in-line structure with the respective coater-developer.
The computers CMP.multidot.En of the exposure apparatus EXPn and those CMP.multidot.Cn of the coater-developers CDn are provided with communication function for example utilizing a RS232C channel, and are connected, through said channel, to personal computers PC1, PC2, . . . , PCn which constitute computers of an intermediate rank and are connected to the host computer H.multidot.COM of the upper rank. Said host computer H.multidot.COM instructs the personal computers PC1, . . . , PCn to execute exposures of wafers with predetermined reticles, and executes the management of entire lithographic process (including wafer logistics management and reticle management) by receiving the information on completed steps from said personal computers.
The personal computers PC1-PCn optimize the processes of the coater-developer CDn and the exposure apparatus EXPn according to the instructions from the host computer H.multidot.COM, and send, to the host computer H.multidot.COM, information on the completed steps and on troubles in the steps. For total management of the IC device production, the host computer H.multidot.COM effects the management of supply of wafers and reticles (logistics management) according to the device to be manufactured, and the calculation of throughput in each exposure apparatus, and controls the entire operation so as to maximize the work rate of each exposure apparatus constituting the production line.
The exposure apparatus employed in the lithographic process lines as shown in FIG. 1 are mostly reduction projection steppers which project the reticle pattern in a reduced size of 1/5 (or 1/10). With the recent development of finer patterns in the semiconductor devices, the precision of manufacture required for the steppers is becoming stricter year after year, and the performance margin (difference between the precision guaranteed by the specifications and the practical precision achievable in stable manner) of the steppers is becoming gradually smaller.
For these reasons, there is being required more refined control enabling, for example:
(A) to collect the details of status of the apparatus (EXPn, CDn) in order to maintain the performance thereof in optimum state;
(B) to restore the performance of the apparatus promptly in case the deterioration in performance is detected; and
(C) to optimize the process parameters for each apparatus or for each lot.
These requirements are only representative ones, but the management of these factors requires gathering, analysis and feedback of enormous data, including the measured performance of various apparatus and the data representing the status during the process.
These operations are practically impossible to execute manually, and the incorporation of the above-mentioned functions (A), (B) and (C) into the host computer H.multidot.COM will result in the following difficulties:
(1) The amount of data to be gathered is excessively large for the capacity of communication channel of the host computer H.multidot.COM designed for production management;
(2) As the host computer is generally designed to control all the process steps, it is generally difficult to incorporate a software for managing and analyzing the detailed data specific to the apparatus solely in the part of lithographic process. It is also difficult to promptly achieve an increase in the number of data items and an improvement in the analyzing algorithm, because of the implication with other managing functions; and
(3) The load of the host computer is inevitably increased, thus limiting other managing functions.